Operational Considerations for Passive Bistatic Radar

Transcription

1 Operational Considerations for Passive Bistatic Radar Presented at 1st RADAR Conference & Exhibition for the Kingdom of Saudi Arabia 8 December 2014 Dr Clayton Stewart Visiting Professor, Electronic and Electrical Engineering, University College London Former Technical Director, US Office of Naval Research Global c.stewart@ucl.ac.uk Dr Hugh Griffiths Professor, Electronic and Electrical Engineering, University College London h.griffiths@ucl.ac.uk UCL ENGINEERING Change the world 1

2 Outline Introduction Background History Passive Bistatic Radar (PBR) System Concept Passive Bistatic Radar (PBR) Waveforms FM radio Analogue TV Digital radio Digital TV Cellphone transmissions Defence and Security Applications of PBR Air surveillance Maritime surveillance Performance Prediction Potential advantages Potential disadvantages Production Systems Lockheed Martin Silent Sentry Thales Homeland Alerter Others

3 Some Background Conventional radar is termed monostatic, i.e. receiver and transmitter are colocated Bistatic radar: transmitter and receiver are separated by some distance PBR: transmitter signal is external to system Original British radar experiment ( Daventry Experiment ) in 1935 by Sir Robert Watson-Watt was PBR Sometimes called Passive Coherent Location (PCL)

4 History of PBR Watson-Watt s experiments in 1935 demonstrated concept First successful use of PBR system by Germany in WWII Klein Heidelberg which exploited British Chain Home radar transmitter Bistatic radar made way for conventional monostatic radar: enabled by development of T/R switch Resurgence in 1980s: emergence of commodity computing LMC Silent Sentry release 1998: 1st commercial product Thales Homeland Alerter 100 ( ) Noticeable resurgence in PBR recently

5 Passive Bistatic Radar Special Issue of IEEE AES Magazine on Passive Radar, Vol.27, No.10, October 2012 Second part in November

6 PBR System Concept reference channel

7 Illuminators of Opportunity PBR systems will use other transmissions that just happen to be there, i.e. illuminators of opportunity, and the technique is sometimes known as - PBR, - hitchhiking, - parasitic radar or - passive coherent location (PCL) Such transmissions may be other radars, or communications, broadcast or navigation signals - In these days of spectral congestion there are more and more such transmissions. Important characteristics of illuminators of opportunity are : - power density at target - coverage (spatial and temporal) and geometry - waveform (frequency, bandwidth, CW carrier)

8 Signal Characteristics of Some Transmitters of Opportunity

9 Air Surveillance Applications Detection of non-emitting and LPI targets Long range border/coastal surveillance Near-range high precision slow and low target tracking Temporary, quick set-up event protection Complement to ATM Gap filler

10 Maritime and Ground Surveillance Applications Harbour awareness and protection Ship detection and tracking Air surveillance Possible ship self protection Border surveillance

11 Advocates of PBR Cite Following Potential Operational Advantages Lower acquisition and O&M costs due to lack of transmitter and moving parts Physically small; easily deployed in places where conventional radars cannot be; operation in difficult terrain Remote, standalone operation possible Allows parts of spectrum (VHF, UHF,...) not usually available for radar Minimised effects from weather conditions Capabilities against stealthy targets: low RF and multistatic geometries Detection of low altitude targets (by diffraction) Rapid updates, typically once a second Covert operation, including no need for frequency allocations Resistant to ESM detection; difficulty of jamming Resilience to ARM s Green radar ; no EM pollution

12 Opponents of PBR Cite Following Potential Operational Disadvantages Technical immaturity Reliance on third-party illuminators; suboptimal waveforms Lower power densities at the target May experience significant RFI 2D operation May experience high false alarm rate Complexity of deployment. Geometries are a critical performance factor Signal content may be inconsistent Typically small receive aperture for low cost, convenience, and covertness: degraded SNR and spatial resolution Fading due to multipath Ghosts possible in multi-target environment Noise floor raised by dense emitter environment Computationally intensive

13 Lockheed Martin Silent Sentry TV and radio stations as illuminators Silicon Graphics processors with multiple gigaflops of processor activity (Aviation Week and Space Technology) ASCIET trials, March System has proven effective to ranges of 220 km Production currently in 3 rd generation Lockheed Martin Corporation

14 Silent Sentry Product Specifications Performance Surveillance Volume Azimuth: Up to 360 Elevation: 60 Continuous Search Range 50 to 100 NM within FOV Targets 100+ simultaneously Aircraft and missiles Accuracy m horizontal position 1000 m vertical position <2 m/s horizontal velocity Data Output SS track format, TADIL-J, or OTH Gold Lockheed Martin Corporation Survivability Operating Environment Room temperature Shelter protected 1.5 kw 120V power Reliability Standard digital component based No moving parts Precipitation All weather antenna Shelter protected equipment Detectability Covert when operating with indigenous illumination Transportability Transport Speed Level highway: speed limit Cross country: 10-15mph Transport Vehicle Shelterized HMMWV or SUV Enclosed truck/suv Grades and Road Conditions VME Rack Ideal for Road Transport Withstands moderate offroad conditions Emplacement Less than 1 day 1-2 person setup

15 Homeland Alerter 100 (Thales, France) In production Introduced at Paris Airshow in 2007 Range : 100km Azimuth : 360 Elevation : 90 Transmitters of opportunity : FM radio, possible extension to DAB, AVB, DVB-T Thales

16 Transportable Passive Radar by Airbus Defence and Space (Formerly Cassidian) EADS Technology Demonstrator unveiled in 2012 Transmitters of opportunity : FM, DAB, DVB Range : test results reported at 250 km bistatic Small ground based targets (cyclist) detected at short range

17 Other PBR Systems CELLDAR CELL PHONE RADAR (BAE Systems Roke, UK) AULOS Passive Covert Location Radar (Selex Sist. Int., Italy) Hellenic Multi-target Passive System HEMPAS or CCIAS ( Thessaloniki Team, Greece): multistatic PCL ESM system Silent Guard FM Radio (ERA, Czech Republic)

18 Conclusion Background and history of PBR PBR waveforms Operational applications of PBR Potential operational advantages and disadvantages Some production and prototype systems

19 Backup

20 Principle In conventional radar, time of transmission is exactly known, allowing target range to be easily calculated PBR does not have this info directly: uses reference receiver to monitor each transmitter being exploited; dynamically sample transmitted waveform. PBR typically employs following processing: Reception of direct signal from transmitter(s) and from surveillance region on dedicated lownoise, linear, digital receivers Digital beamforming to determine DOA of signals and spatial rejection of strong in-band interference. Adaptive filtering to cancel any unwanted direct signal returns in the surveillance channel(s). Transmitter-specific signal conditioning Cross-correlation of reference channel with surveillance channel to determine object bistatic range and Doppler. Detection using CFAR. Association and tracking of object returns in range/doppler space, known as line tracking. Association and fusion of line tracks from each transmitter to form final estimate of targets location, heading and speed.

21 PBR Geometry target R R R T R transmitter L receiver R R 2 R R Lsin 2 2 R R L T R T R R Jackson, M.C., The geometry of bistatic radar systems ; IEE Proc., Vol.133, Pt.F, No.7, pp , December 1986.

22 PBR Geometry Contours of constant bistatic range are ellipses, with transmitter and receiver as foci target RT RR transmitter L = bistatic baseline receiver R T + R const R Targets lying on the transmitter-receiver baseline have zero bistatic range.

23 Typical Illuminators (30 MHz 3 GHz) PBR systems have been developed that exploit following sources of illumination: Analog TV FM radio ( MHz) Cellular phone base stations Digital Audio Broadcasting (DAB MHz) Digital Video Broadcasting Terrestrial (DVB-T including MHz and 300 MHz 3 GHz sub-bands) Terrestrial high definition TV (North America) GPS satellites Satellite signals have generally been found to be inadequate for passive radar use: either because powers are too low, or because orbits of satellites are such that illumination is too infrequent. Possible exception to this is the exploitation of satellite-based radar and satellite radio systems

24 Generic PBR Signal Processing Scheme Wikipedia

25 What Was NATO SET-164? Primary achievement of SET-164: analysis of bistatic VHF clutter obtained from FM radio based PBR data. RCS values and statistical distributions have been derived These can be used in system specifications and operational analysis studies. SET-164 has also undertaken a feasibility study of a number of important applications for PBR: Harbour protection for Maritime Situational Awareness (MSA). Bistatic SAR (BSAR) using satellites to increase military benefit when using satellite-borne illuminators. Civil ATM and military air surveillance using PBR 25

26 Passive SAR System Transmitter (RADARSAT1/2, future Sentinel) Goal: produce images/interferograms Receiver (C-band) Capt Virginie Kubica, Belgium RMA